Fractionation of c12 bicycle aromatic hydrocarbons by 2-chloro,4-nitrobenzoic acid complex formation

ABSTRACT

Mixtures of C12 bicyclic aromatic hydrocarbons containing dimethylnaphthalenes are difficult to fractionate by conventional techniques such as distillation or crystallization. However, by dissolving 2-chloro, 4-nitrobenzoic acid in such a mixture at an elevated temperature, followed by subsequent cooling, a solid complex of said acid and certain hydrocarbons is formed. Separation of the solid complex from the cooled mixture and its subsequent decomposition results in a product that is substantially richer in those dimethylnaphthalenes which have greater tendency to form such complexes. Upon further processing, these dimethylnaphthalenes have utility in the production of dyes.

United States Patent [151 3,665,044 Scott [4 May 23, 1972 [54]FRACTIONATION OF C12 BICYCLE AROMATIC HYDROCARBONS BY 2- CHLORO,4-NITROBENZOIC ACID COMPLEX FORMATION [72] Inventor: Kenneth A. Scott,Swarthmore, Pa.

[73] Assignee: Sun Oil Company, Philadelphia, Pa.

[22] Filed: May 1, 1970 [21] Appl. No.: 33,951

[52] US. Cl. ..260/674 N [51] Int. Cl ...C07c 7/00 [58] Field of Search..260/674 N [56] References Cited UNITED STATES PATENTS 2,941,017 6/1960Veatch et a1 ..260/674 3,249,644 3/1966 Hahn ..260/674 PrimaryExaminerDelbert E. Gantz Assistant Examiner-C. E. SpresserAtt0rney-George L. Church, Donald R. Johnson and Wilmer E. McCorquodale,Jr.

[ ABSTRACT Mixtures of C bicyclic aromatic hydrocarbons containingdimethylnaphthalenes are difiicult to fractionate by conventionaltechniques such as distillation or crystallization. However, bydissolving 2-chloro, 4-nitrobenzoic acid in such a mixture at anelevated temperature, followed by subsequent cooling, a solid complex ofsaid acid and certain hydrocarbons is formed. Separation of the solidcomplex from the cooled mixture and its subsequent decomposition resultsin a product that is substantially richer in those dimethylnaphthaleneswhich have greater tendency to form such complexes. Upon furtherprocessing, these dimethylnaphthalenes have utility in the production ofdyes.

5 Claims, No Drawings FRACTIONATION OF C1: BICYCLE AROMATIC HYDROCARBONSBY Z-CI'ILORO, 4-NITROBENZOIC ACID COMPLEX FORMATION CROSS REFERENCES TORELATED APPLICATIONS 5 lnventor(s) Title 33,949 R. 1. Davis 33,950 R. I.Davis BACKGROUND OF THE INVENTION The invention relates generally to aprocess for fractionating difiicult-to-separate C bicyclic aromatichydrocarbons and in particular the isomers of dimethylnaphthalenes. Morespecifically, it relates to a process for fractionating isomers ofdimethylnaphthalene by initially dissolving 2-chloro, 4- nitrobenzoicacid in the liquid hydrocarbons.

Dimethylnaphthalenes are oxidized to naphthalene-carboxylic acids whichare used in the production of dyes and pigments. A more detaileddiscussion of the utility of dimethylnaphalenes appears inNaphthalenecarboxylic Acids by K. A. Scott in Kirk-Othmer, Encyclopediaof Chemical Technology, 2nd Edition, Vol. 13.

For convenience dimethylnaphthalene or dimethylnaphthalenes herein willbe referred to as DMN with specific DMN isomers being indicated byreference to the location of the methyl groups. For example,2,6-dimethylnaphthalene will be referred to as 2,6-DMN.

DMN are found in coal tar, lignite tar, crude oil, the drip-oil fractionproduced during the pyrolysis of hydrocarbons to make olefins, in heavypetroleum reformate and in petroleum gas oil produced by catalyticcracking. In these hydrocarbon mixtures DMN are usually present inrather dilute concentration. For example, one analysis shows DMN makingup about 4 percent by weight of a gas oil. However, by known processessuch as distillation, crystallization and solvent extraction, DMN can berecovered in concentrated form from the previously mentioned sources. Inoxidizing these DMN to carboxylic acids, it is usually preferable thateach isomer be oxidized by itself since generally each isomer requiresslightly different reaction conditions for optimum oxidation.

Most, if not all, the isomers of DMN usually are present in thesehydrocarbon mixtures. These DMN isomers, as well as certain other Calkylnaphthalenes such as ethylnaphthalenes, have boiling points whichare extremely close to each other. This closeness in boiling pointsmakes it extremely difficult to distill apart the individual isomers ordistill some isomers from other C alkylnaphthalenes. These boilingpoints are as follows:

C, Alkylnaphthalenes Boiling Points, F.

2-ethylnaphthalene 496 l-ethylnaphthalene 498 2,6-DMN 504 2,7-DMN 5041,7-DMN 505 1,6-DMN SOS 1,3-DMN 509 1,5-DMN 509 1,2-DMN 514 2,3-DMN 5161,4-DMN 515 1,8-DMN 518 AH Project 44, Tables 232(33.5200),232(33.52 10)and 23-2-( 33.5211) Since 2,6-DMN and 2,7-DMN have the same boilingpoints, these isomers cannot be separated by distillation. Other suchpairs are 1,7-DMN and 1,6-DMN, as well as 1,3-DMN and 1,5-DMN.

Certain DMN isomers can be separated using the differences in theirfreezing points. These methods are reported in U.S. Pat. No. 3,202,726issued Aug. 24, 1965 to E. W. Malmberg eta]. and U.S. Pat. No. 3,173,960issued Mar. 16, 1965 to W. M. Robinson. However, despite differences infreezing points, various DMN isomers form eutectics, making itimpossible to further separate these isomers by crystallization. Forexample, 2,6-DMN with a freezing point of 234 F. and 2,3-DMN with afreezing point of22l F. form a eutectic with a freezing point of about170 F. Thus other methods besides crystallization and distillation areneeded for separating various DMN isomers from each other.

Other techniques have been suggested for purification and/or separationof DMN. U.S. Pat. No. 3,183,279 issued May 11, 1965 to l. W. Mills eta1. uses selective oxidations; U.S. Pat. No. 3,155,739 issued Nov. 3,1964 to G. Suld uses a HF-BF complex. Still others have facilitatedseparation and/or purification by isomerizing various DMN isomers tospecific isomers (See J. Org. Chem, 29, 2939-2946, 1964, G. Suld etal.)

Summarizing, the separation of DMN isomers from each other by knownmethods is difficult if not practically impossible. There is a need foranother purification and/or separation method or a method whichfacilitates existing procedures.

' SUMMARY OF THE INVENTION This invention provides a process for thefractionation of C bicyclic aromatic hydrocarbons containing DMN byselective complexation with 2-ch1oro, 4-nitrobenzoic acid. The acid isdissolved in the hydrocarbon mixture containing DMN, preferably at anelevated temperature. Afterwards, the resulting solution is cooled to alower temperature and the formed solid acid-DMN complex is separated.The complex is decomposed by known methods and the subsequently releasedDMN has a composition substantially different from the startinghydrocarbon mixture.

DESCRIPTION The complexing agent, 2-chloro, 4-nitrobenzoic acid, forconvenience, is referred to herein as CNA. This acid is added, either asa solid or melt, to the C bicyclic aromatic hydrocarbons mixturecontaining DMN. The C liquid, during this addition, can be at eitherambient or elevated temperature. However, if the resultingacid-hydrocarbon mixture remains at ambient temperature, i.e., 50 to F.,the rate at which the acid dissolves is very slow and the amountultimately dissolved is very small. The small amount of acid that goesinto solution at ambient temperature can be recovered as solidacidhydrocarbon complex by lowering the temperature of the mixture,e.g., to 0 F. However, the preferred method involves using a temperaturewhich is sufficiently high so that substantially all the added CNA willrapidly dissolve. While temperatures higher than the normal boilingpoint of the C bicyclic aromatic hydrocarbon mixture can be used todissolve the acid by employing elevated pressures, it is desirable thata lower temperature be used, preferably below the boiling point of the Cmixture and more preferably below the boiling point of the DMN.

After the CNA has dissolved, the solution is allowed to cool to to 100F. either with or without agitation. During this cooling step, a solidcomes out of solution. This solid is a complex of CNA and DMN. Thissolid complex is separated from the liquid by conventional methods suchas filtration or decantation.

It is believed that the complexes formed herein are 1r complexes, i.e.,they are caused by combination between the 11 electrons of the two ringsinvolved. The CNA apparently accepts a share in the 1r electrons of thecompound which is complexed with it. Steric factors appear to have astrong effect, since according to the theory of w complex formation, thetwo rings must be close together and parallel in order for the complexto form. These complexes are distinct from the acid-base type asexemplified by complexes of HF'BF and xylenes and also from clathratecomplexes of, for example, the urea-paraffin type.

Some DMN isomers complex more readily than others with CNA. Thesedifferences in tendencies to form complexes can be used to facilitatefractionation of DMN isomers.

The feed to this process can include, in addition to at least two DMNisomers, other compounds that do not alter or destroy the structure ofthe complex. In general, appreciable quantities of undesirable compoundsthat will react with the acid are to be avoided. Compounds such as C, toC alkanes, alkenes, cycloalkanes, cycloalkenes or mixtures thereof arerelatively inert and have no appreciable effect on the complexformation. However, hydrocarbons boiling outside the boiling range of Cbicyclic aromatic hydrocarbons and which form complexes with this acidshould not be present in appreciable quantities in the feed. Forexample, a Czechoslovakian reference, J. Slosar and V. Sterba, Chem.Prumysl., l/40(3), pages 142-147 91965), teaches the use of 2-chloro, 4-nitrobenzoic acid as a means of isolating l-methylnaphthalene. Thismethylnaphthalene can be excluded from the feed to the present processby using a feed having only C bicyclic aromatic hydrocarbons containingDMN. Preferably, C bicyclic aromatic hydrocarbons are Calkylnaphthalenes and ideally they are only DMN.

The amount of CNA employed in the complexing step can vary over a widerange depending upon the fractionation desired. The amount of CNA isrelated to the amount of DMN present. Preferably, the amount of CNAdissolved in the hydrocarbon mixture is in the range from 0.01 to 3.0moles of CNA per mole of DMN. A preferred narrower range is from 0.10 to1.5 moles of CNA per mole of DMN. The contacting of the C bicyclicaromatic hydrocarbons with CNA can be performed in one contacting stageor a plurality of distinct contacting stages.

The temperature above which the acid rapidly dissolves in thehydrocarbon mixture being treated can be determined by simply heating amixture of the two while agitating and observing the temperature levelat which rapid dissolution occurs. 1 have found, for example, that thepreferred temperature for dissolving the acid in a C bicyclic aromatichydrocarbon mixture containing DMN is at a temperature 250 to 400 F.,more preferably between 300 to 400 F. Agitation is helpful to dissolvethe CNA.

While not all the acid added to the hydrocarbon mixture need go intosolution, it is preferred that substantially all of it does. Sinceundissolved acid does not complex with DMN, any undissolved, aciddecreases the amount of complexation per mole of added acid and thisdecrease in complexation is undesirable.

After the acid has gone into solution, the solution is cooled, with orwithout agitation, until the CNA-DMN crystallizes out.

The solid complex is readily separated from the resulting admixture.Filtration, decantation or centrifugation can be used to remove thecomplex. Separation of the complex from the admixture is ordinarilyperformed at a temperature below about 150 F.; temperatures between 50and 125 F. are particularly effective for CNA-DMN complex separation.Lower separation temperatures, e.g. 0 F., can also be used.

After separation, it is advisable to wash the complex with a lighthydrocarbon solvent in order to remove the physically absorbed liquidmixture from the complex, after which the complex is vacuum dried.Pentance is an excellent wash solvent.

Several techniques can be employed to decompose the solid complex. Thepreferred procedure comprises heating the solid complex to a temperaturewhereby the complex is decomposed and the DMN are obtained as adistillate. The recovered acid can be recycled to the same or anothercontacting zone.

A second procedure for decomposing the complex involves heating in thepresence of an inert solvent, such as C to C alkanes, alkenes,cycloalkanes, cycloalkenes or mixtures thereof, whereby the complexdecomposes and two layers are formed one consisting of the complexingacid and the other of a solution of the DMN in a solvent. Accordingly,if a low boiling alkane, for example, is used as a solvent, it may benecessary to use superatmospheric pressure in order to maintain thenecessary decomposition temperature. The recovered DMN can be separatedfrom the solution by evaporating the solvent.

A third procedure for decomposing the complex is to contact it withwater or an aqueous base, such as aqueous sodium hydroxide. With theaqueous base, the acid becomes a salt in the resulting water layer andthe organic layer is DMN. The salt in the water layer facilitates theseparation of the two layers.

The following example illustrates the invention:

EXAMPLE The CNA used was white crystals having a melting point of 283 to286 F. The composition of the hydrocarbon mixture treated to illustratethis invention is shown in the following Table and is referred to asfeed.

The feed was treated in the following manner. One mole of CNA per 5moles of DMN present in the feed was added to the feed at roomtemperature. All the crystals of CNA did not dissolve. The mixture washeated and agitated at about 300 F. until a solution had formed, i.e.,all the CNA had disappeared. The resulting solution was allowed to cool.During this cooling period, the complex crystallized out. The solidcomplex was filtered out and subsequently washed and vacuum dried. Afterthis washing and drying, the solid complex was placed in 10 percentaqueous sodium hydroxide and then heated until an organic layer wasformed. This organic layer is the complexate containing a differentpercentage of DMN than the feed.

Also shown in the following Table are the ratios (weight or mole) ofeach specific DMN in the complexate to the same DMN in thenoncomplexate. If this ratio equals one, no change in concentrationoccurred. If this ratio is greater than one, complexation of thespecific DMN was preferential and if less than one, complexation of thespecific DMN was not preferential.

TABLE Formation of DMN-CNA Complexes l,2-DMN 0.6 1.7 0.2 8.5 2,3-DMN 1.33.1 0.6 5.2

TOTAL lOO.l 100.0 100.0

The data in the foregoing Table show that certain DMN complex to agreater extent than others. Thus, for example, the ratio of 1,7-DMN inthe complexate to the same DMN in the noncomplexate is 1.7, whereas theratio of 2,6-D1VIN in the complexate to the same DMN in thenoncomplexate is 0.56.

C bicyclic aromatic hydrocarbon mixtures containing DMN, other than theaforementioned feed, can be fractionated in an analogous manner usingthe acid as a selective complexing agent.

The invention claimed is:

1. A method of fractionating a liquid mixture of C bicyclic aromatichydrocarbons having a major amount of C alkylnaphthalenes and containingdimethylnaphthalenes comprismg:

a. dissolving 2-chloro, 4-nitrobenzoic acid in said mixture at atemperature at which it is liquid to complex preferentially with atleast one of the dimethylnaphthalenes and form a complex containing lessthan the total amount of dimethylnaphthalenes;

b. cooling the resulting hydrocarbon-acid solution until solid complexof dimethylnaphthalenes and acid crystal- 6 lizes;

c. separating the solid complex from the resulting admixture;

d. and decomposing the solid complex to recover the resulting complexatehaving a proportion of dimethylnaphthalenes different from that in thestarting hydrocarbon mixture.

2. A method according to claim 1 wherein the mixture of C bicyclicaromatic hydrocarbons consists essentially of a mixture of Calkylnaphthalenes containing dimethylnaphthalenes.

3. A method according to claim 1 wherein the mixture of hydrocarbonsconsists essentially of a mixture of dimethylnaphthalenes.

4. A method according to claim 1 wherein the amount of acid dissolved insaid hydrocarbon mixture is in the range from 0.01 to 3.0 moles per moleofdimethylnaphthalenes.

5. A method according to claim 1 wherein the mixture of saidhydrocarbons consists essentially of C alkylnaphthalenes containingdimethylnaphthalenes, the amount of acid dissolved in saidalkylnaphthalenes is in the range from 0.1 to 1.5 moles per mole ofdimethylnaphthalenes, the dissolving occurs at a temperature in therange from 300 to 400 F. and the solid complex is separated at 0 to F.

2. A method according to claim 1 wherein the mixture of C12 bicyclicaromatic hydrocarbons consists essentially of a mixture of C12alkylnaphthalenes containing dimethylnaphthalenes.
 3. A method accordingto claim 1 wherein the mixture of hydrocarbons consists essentially of amixture of dimethylnaphthalenes.
 4. A method according to claim 1wherein the amount of acid dissolved in said hydrocarbon mixture is inthe range from 0.01 to 3.0 moles per mole of dimethylnaphthalenes.
 5. Amethod according to claim 1 wherein the mixture of said hydrocarbonsconsists essentially of C12 alkylnaphthalenes containingdimethylnaphthalenes, the amount of acid dissolved in saidalkylnaphthalenes is in the range from 0.1 to 1.5 moles per mole ofdimethylnaphthalenes, the dissolving occurs at a temperature in therange from 300* to 400* F. and the solid complex is separated at 0* to125* F.